feat(android): add gallery app integration (#1695)

[tobikrs]

Fixes #1695

Memories did not appear in the Android system gallery chooser when tapping a camera
thumbnail, using "Open with" from a file manager, or selecting media in app pickers.

Approach

A new ViewerActivity is registered as the entry point for all incoming media intents.
On launch it resolves the incoming content:// URI against MediaStore and the local
Room DB, then routes to one of three modes:

• Mode A (user is logged in + file is synced): redirects to MainActivity with a
  #v/{dayId}/{localId} hash, opening the photo directly in the Memories WebView viewer.
  ViewerActivity finishes immediately and is never visible.
• Mode B (file not synced / offline): full-screen native viewer with ViewPager2 swipe
  navigation, pinch-zoom images (PhotoView), video playback (ExoPlayer), share, and delete.
  An "Open in Memories" FAB triggers the Mode A redirect when the user later logs in.
• Mode C (picker intent): same native viewer as Mode B, but the toolbar shows a
  "Use this" action instead of share/delete, and returns the URI to the calling app via
  setResult.

Intent filters added to ViewerActivity

Action	Use case
com.android.camera.action.REVIEW	Camera thumbnail tap (legacy camera apps)
android.provider.action.REVIEW	Camera thumbnail tap (Android 10+ / Google Camera)
ACTION_VIEW image/* + video/*	"Open with" from file manager or share sheet
ACTION_PICK	Media picker (e.g. attach photo in messaging apps)
ACTION_GET_CONTENT	Media picker (alternative intent)

MainActivity is changed to singleTask so that a Mode A redirect brings the existing
instance to the foreground rather than creating a second one.

Other changes

• MediaResolverService: resolves a content:// URI to structured media metadata
  (MediaStore _ID, auid, dayId, MIME type) by querying MediaStore then Room DB.
• PlayerController: ExoPlayer logic extracted from MainActivity into a reusable
  class (local URIs, remote HTTP/HLS, error fall-through). Both MainActivity and
  ViewerActivity use it.
• MainActivity: gains a pendingPhotoHash field consumed in onNewIntent(),
  loadDefaultUrl(), and onPageFinished() to handle the Mode A deep-link reliably
  regardless of whether the WebView has already finished loading.
• PhotoView (com.github.chrisbanes:PhotoView:2.3.0) added as dependency for pinch-zoom.

Reviewer notes

• Mode A uses the URL hash as the deep-link mechanism because it is the only way to open
  a specific photo in the Memories frontend (Vue Router watches #v/{dayId}/{fileid}).
• In Mode B, swipe navigation loads all photos for the same day from Room DB and positions
  the pager at the current photo. When the file is not in the DB, a single-item pager is
  shown with swiping disabled.
• Delete uses MediaStore.createTrashRequest() on API 30+ and direct deletion on older
  versions. On success the item is removed from the pager; if no items remain, the activity
  finishes.